h magnitudes, distance 50", p.
170 deg..

The brilliant constellations of Gemini and Taurus tempt us next, but
warning clouds are gathering, and we shall do well to house our
telescopes and warm our fingers by the winter fire. There will be other
bright nights, and the stars are lasting.

CHAPTER III

FROM GEMINI TO LEO AND ROUND ABOUT

"If thou wouldst gaze on starry Charioteer,
And hast heard legends of the wondrous Goat,
Vast looming shalt thou find on the Twins' left,
His form bowed forward."--POSTE'S ARATUS.

[Illustration: MAP NO. 4.]

The zodiacal constellations of Gemini, Cancer, and Leo, together with
their neighbors Auriga, the Lynx, Hydra, Sextans, and Coma Berenices,
will furnish an abundance of occupation for our second night at the
telescope. We shall begin, using our three-inch glass, with alpha, the
chief star of Gemini (map No. 4). This is ordinarily known as Castor.
Even an inexperienced eye perceives at once that it is not as bright as
its neighbor Pollux, beta. Whether this fact is to be regarded as
indicating that Castor was brighter than Pollux in 1603, when Bayer
attached their Greek letters, is still an unsettled question. Castor may
or may not be a variable, but it is, at any rate, one of the most
beautiful double stars in the heavens. A power of one hundred is amply
sufficient to separate its components, whose magnitudes are about two
and three, the distance between them being 6", p. 226 deg.. A slight yet
distinct tinge of green, recalling that of the Orion nebula, gives a
peculiar appearance to this couple. Green is one of the rarest colors
among the stars. Castor belongs to the same general spectroscopic type
in which Sirius is found, but its lines of hydrogen are broader than
those seen in the spectrum of the Dog Star. There is reason for
thinking that it may be surrounded with a more extensive atmosphere of
that gaseous metal called hydrogen than any other bright star possesses.
There seems to be no doubt that the components of Castor are in
revolution around their common center of gravity, although the period is
uncertain, varying in different estimates all the way from two hundred
and fifty to one thousand years; the longer estimate is probably not far
from the truth. There is a tenth-magnitude star, distance 73", p. 164 deg.,
which may belong to the same system.

From Castor let us turn to Pollux, at the same time exchanging our
three-inch telescope for the four-inch,